With reference to street lighting, how do sodium lamps differ from LED lamps?
- Sodium lamps produce light in 360 degrees but it is not so in the case of LED lamps.
- As street-lights, sodium lamps have longer life span than LED lamps.
- The spectrum of visible light from sodium lamps is almost monochromatic while LED lamps offer significant colour advantages in street lighting.
Select the correct answer using the code given below
Detailed Explanation:
Answer: Option 3 — 1 and 3
This question compares traditional sodium lamps with modern LED lamps used in street lighting. Statement 1 correctly identifies that sodium lamps emit light omnidirectionally (360 degrees), while LEDs are directional, reducing light wastage. Statement 3 correctly notes that sodium lamps produce nearly monochromatic yellow light, whereas LEDs offer better color rendering and spectrum diversity.
✅ Statement 1 – Correct: Sodium lamps emit light in all directions (360 degrees), while LED lamps are directional and focus light where needed, improving efficiency.
❌ Statement 2 – Incorrect: LED lamps have a significantly longer lifespan (50,000-100,000 hours) compared to sodium lamps (15,000-24,000 hours).
✅ Statement 3 – Correct: Sodium lamps produce monochromatic yellow-orange light (narrow spectrum), while LED lamps offer a broad spectrum with better color rendering index (CRI) for street lighting.
📝 Short Notes: Street Lighting Technologies
| Parameter | Sodium Lamps (HPS/LPS) | LED Lamps |
|---|---|---|
| Light Distribution | Omnidirectional (360°) - requires reflectors | Directional - focused beam |
| Lifespan | 15,000-24,000 hours | 50,000-100,000 hours |
| Light Spectrum | Monochromatic (yellow-orange) | Full spectrum, adjustable |
| Color Rendering Index (CRI) | Low (20-25) | High (70-90+) |
| Energy Efficiency | Moderate (80-140 lm/W) | High (100-200 lm/W) |
| Warm-up Time | Several minutes | Instant on/off |
| Environmental Impact | Contains mercury/sodium | No hazardous materials |
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